Thermoplastic membranes containing expandable graphite

ABSTRACT

A multi-layered membrane comprising a first thermoplastic first layer and a second thermoplastic layer, where the second layer includes expandable graphite.

This application claims the benefit of U.S. Non-Provisional applicationSer. No. 13/799,763, filed on Mar. 13, 2013, and U.S. ProvisionalApplication Ser. No. 61/727,354, filed on Nov. 16, 2012, which areincorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the present invention are directed toward thermoplasticcompositions containing expandable graphite and the use of thesecompositions in roofing membranes.

BACKGROUND OF THE INVENTION

Flat or low-sloped roofs are often covered with polymeric membranes.Common among the membranes that have the mechanical properties needed tobe technologically useful are thermoset membranes prepared with EPDMrubber, or thermoplastic membranes prepared with ethylene-propylenereactor copolymers or blends of polyethylene and polypropylene. Thesemembranes typically contain carbon black and/or mineral fillers, whichprovide advantageous mechanical properties to the membranes.

Many roofs, especially flat or low-sloped roofs, are covered with apolymeric membrane. Polymeric membranes used in these applicationsinclude both thermoset membranes and thermoplastic membranes. Exemplarythermoset membranes include EPDM rubber. Thermoplastic membranes includePVC membranes and olefinic-based thermoplastic membranes. Olefinic-Basedthermoplastic membranes offer unique advantages, including the abilityto extrude the membrane, which facilitates manufacturing, and theability to heat weld the membranes to form a continuous water barrier onthe roofing surface.

Because the olefinic-based membranes are rich in hydrocarbon content,they may require significant flame retardants to pass industry andgovernmental flame and/or fire standards. The use of these flameretardants can have some drawbacks including cost and loss of mechanicalproperties.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a multi-layered membranecomprising a first thermoplastic first layer and a second thermoplasticlayer, where the second layer includes expandable graphite.

Embodiments of the present invention provide multi-layered thermoplasticmembrane comprising at least one thermoplastic layer having dispersedtherein expandable graphite.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a multi-layered membrane including twoco-extruded laminated layers according to embodiments of the presentinvention.

FIG. 2 is a perspective view of a multi-layered membrane including twolaminated layers according to embodiments of the present invention.

FIG. 3 is a perspective view of a laminate membrane according toembodiments of the present invention.

FIG. 4 is a perspective, cross sectional view of a roof assemblyaccording to embodiments of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the present invention are based, at least in part, on thediscovery of a thermally-processable composition that includesexpandable graphite dispersed within a thermoplastic matrix. It hasadvantageously been discovered that these compositions can be used tofabricate one or more layers of multi-layered, single-ply membranes thatare useful, among other things, as roofing membranes and geomembranes.

Expandable Graphite

In one or more embodiments, expandable graphite, which may also bereferred to as expandable flake graphite, intumescent flake graphite, orexpandable flake, includes intercalated graphite in which anintercallant material is included between the graphite layers ofgraphite crystal or particle. Examples of intercallant materials includehalogens, alkali metals, sulfates, nitrates, various organic acids,aluminum chlorides, ferric chlorides, other metal halides, arsenicsulfides, and thallium sulfides. In certain embodiments of the presentinvention, the expandable graphite includes non-halogenated intercallantmaterials. In certain embodiments, the expandable graphite includessulfate intercallants, also referred to as graphite bisulfate. As isknown in the art, bisulfate intercalation is achieved by treating highlycrystalline natural flake graphite with a mixture of sulfuric acid andother oxidizing agents which act to catalyze the sulfate intercalation.

Commercially available examples of expandable graphite include HPMSExpandable Graphite (HP Materials Solutions, Inc., Woodland Hills,Calif.) and Expandable Graphite Grades 1721 (Asbury Carbons, Asbury,N.J.). Other commercial grades contemplated as useful in the presentinvention include 1722, 3393, 3577, 3626, and 1722HT (Asbury Carbons,Asbury, N.J.).

In one or more embodiments, the expandable graphite may be characterizedas having a mean or average size in the range from about 30 μm to about1.5 mm, in other embodiments from about 50 μm to about 1.0 mm, and inother embodiments from about 180 to about 850 μm. In certainembodiments, the expandable graphite may be characterized as having amean or average size of at least 30 μm, in other embodiments at least 44μm, in other embodiments at least 180 μm, and in other embodiments atleast 300 μm. In one or more embodiments, expandable graphite may becharacterized as having a mean or average size of at most 1.5 mm, inother embodiments at most 1.0 mm, in other embodiments at most 850 μm,in other embodiments at most 600 μm, in yet other embodiments at most500 μm, and in still other embodiments at most 400 μm. Useful expandablegraphite includes Graphite Grade #1721 (Asbury Carbons), which has anominal size of greater than 300 μm.

In one or more embodiments of the present invention, the expandablegraphite may be characterized as having a nominal particle size of 20×50(US sieve). US sieve 20 has an opening equivalent to 0.841 mm and USsieve 50 has an opening equivalent to 0.297 mm. Therefore, a nominalparticle size of 20×50 indicates the graphite particles are at least0.297 mm and at most 0.841 mm.

In one or more embodiments, the expandable graphite may be characterizedas having a carbon content in the range from about 75% to about 99%. Incertain embodiments, the expandable graphite may be characterized ashaving a carbon content of at least 80%, in other embodiments at least85%, in other embodiments at least 90%, in yet other embodiments atleast 95%, in other embodiments at least 98%, and in still otherembodiments at least 99% carbon.

In one or more embodiments, the expandable graphite may be characterizedas having a sulfur content in the range from about 0% to about 8%, inother embodiments from about 2.6% to about 5.0%, and in otherembodiments from about 3.0% to about 3.5%. In certain embodiments, theexpandable graphite may be characterized as having a sulfur content ofat least 0%, in other embodiments at least 2.6%, in other embodiments atleast 2.9%, in other embodiments at least 3.2%, and in other embodiments3.5%. In certain embodiments, the expandable graphite may becharacterized as having a sulfur content of at most 8%, in otherembodiments at most 5%, in other embodiments at most 3.5%.

In one or more embodiments, the expandable graphite may be characterizedas having an expansion ratio (cc/g) in the range from about 10:1 toabout 500:1, in other embodiments at least 20:1 to about 450:1, in otherembodiments at least 30:1 to about 400:1, in other embodiments fromabout 50:1 to about 350:1. In certain embodiments, the expandablegraphite may be characterized as having an expansion ratio (cc/g) of atleast 10:1, in other embodiments at least 20:1, in other embodiments atleast 30:1, in other embodiments at least 40:1, in other embodiments atleast 50:1, in other embodiments at least 60:1, in other embodiments atleast 90:1, in other embodiments at least 160:1, in other embodiments atleast 210:1, in other embodiments at least 220:1, in other embodimentsat least 230:1, in other embodiments at least 270:1, in otherembodiments at least 290:1, and in yet other embodiments at least 300:1.In certain embodiments, the expandable graphite may be characterized ashaving an expansion ratio (cc/g) of at most 350:1, and in yet otherembodiments at most 300:1.

In one or more embodiments, the expandable graphite, as it exists withthe thermoplastic component of the thermoplastic membrane of the presentinvention, may be partially expanded. In one or more embodiments, theexpandable graphite is not expanded, however, to a deleterious degree,which includes that amount or more of expansion that will deleteriouslyimpact the ability to form the sheet product and/or the ability of thegraphite to serve as flame retardant at desirable levels, which includethose levels that allow proper formation of the sheet. In one or moreembodiments, the expandable graphite is expanded to at most 60%, inother embodiments at most 50%, in other embodiments at most 40%, inother embodiments at most 30%, in other embodiments at most 20%, and inother embodiments at most 10% beyond its original unexpanded size.

In one or more embodiments, the expandable graphite may be characterizedas having a pH in the range from about 1 to about 10; in otherembodiments from about 1 to about 6; and in yet other embodiments fromabout 5 to about 10. In certain embodiments, the expandable graphite maybe characterized as having a pH in the range from about 4 to about 7. Inone or more embodiments, the expandable graphite may be characterized ashaving a pH of at least 1, in other embodiments at least 4, and in otherembodiments at least 5. In certain embodiments, the expandable graphitemay be characterized as having a pH of at most 10, in other embodimentsat most 7, and in other embodiments at most 6.

In one or more embodiments, the expandable graphite may be characterizedby an onset temperature ranging from about 100° C. to about 250° C.; inother embodiments from about 160° C. to about 225° C.; and in otherembodiments from about 180° C. to about 200° C. In one or moreembodiments, the expandable graphite may be characterized by an onsettemperature of at least 100° C., in other embodiments at least 130° C.,in other embodiments at least 160° C., and in other embodiments at least180° C. In one or more embodiments, the expandable graphite may becharacterized by an onset temperature of at most 250° C., in otherembodiments at most 225° C., and in other embodiments at most 200° C.Onset temperature may also be interchangeably referred to as expansiontemperature; and may also be referred to as the temperature at whichexpansion of the graphite starts.

Complementary Flame Retardants

In one or more embodiments, the expandable graphite may be used inconjunction with a complementary flame retardant. These complementaryflame retardants may include any compound that increases the burnresistivity, particularly flame spread such as tested by UL 94 and/or UL790, in the polymeric compositions of the present invention. Generally,useful flame retardants include those that operate by forming achar-layer across the surface of a specimen when exposed to a flame.Other flame retardants include those that operate by releasing waterupon thermal decomposition of the flame retardant compound. Useful flameretardants may also be categorized as halogenated flame retardants ornon-halogenated flame retardants.

Exemplary non-halogenated flame retardants include magnesium hydroxide,aluminum trihydrate, zinc borate, ammonium polyphosphate, melaminepolyphosphate, and antimony oxide (Sb₂O₃). Magnesium hydroxide (Mg(OH)₂)is commercially available under the tradename Vertex™ 60, ammoniumpolyphosphate is commercially available under the tradename Exolite™ AP760 (Clarian), melamine polyphosphate is available under the tradenameBudit™ 3141 (Budenheim), and antimony oxide (Sb₂O₃) is commerciallyavailable under the tradename Fireshield™.

Examples of other complementary calcium borate, magnesium hydroxide,basic magnesium carbonate, aluminum trihydrate, zinc borate, gypsum, andmixtures thereof. In these or other embodiments, the complementary flameretardant includes colemanite, which is a borate mineral that isbelieved to include about 50-80% calcium borate.

Thermoplastic Matrix Polymers

In one or more embodiments, the thermoplastic matrix includes one ormore thermoplastic polymers. In one or more embodiments, thethermoplastic polymers include a thermoplastic polyolefin. Otherthermoplastic materials include thermoplastic vulcanizates,propylene-based elastomers, ethylene-based elastomers, thermoplasticeleastomers (e.g. block copolymers), ethylene vinyl acetate, ethylenealkyl acrylates, and mixtures thereof.

Thermoplastic polyolefin polymers include polymers and copolymersincluding one or more mer units deriving from olefinic monomer. Blendsof polymers may also be used. These blends include physical blends aswell as reactor blends. In one or more embodiments, the thermoplasticpolyolefin polymers may derive from recycled thermoplastic polyolefinmembranes as described in copending application Ser. No. 11/724,768,which is incorporated herein by reference.

In one or more embodiments, the thermoplastic polyolefin polymers mayinclude an olefinic reactor copolymer, which may also be referred to asin-reactor copolymer. Reactor copolymers are generally known in the artand may include blends of olefinic polymers that result from thepolymerization of ethylene and α-olefins (e.g., propylene) with sundrycatalyst systems. In one or more embodiments, these blends are made byin-reactor sequential polymerization. Reactor copolymers useful in oneor more embodiments include those disclosed in U.S. Pat. No. 6,451,897,which is incorporated therein by reference. Reactor copolymers, whichare also referred to as TPO resins, are commercially available under thetradename HIFAX™ (Lyondellbassel); these materials are believed toinclude in-reactor blends of ethylene-propylene rubber and polypropyleneor polypropylene copolymers. In one or more embodiments, the in-reactorcopolymers may be physically blended with other polyolefins. Forexample, in reactor copolymers may be blended with linear low densitypolyethene.

In other embodiments, the thermoplastic polyolefin polymers may includeone or more polyolefins such as, but not limited to, propylene-basedthermoplastic polymers, plastomers, and/or ethylene-based thermoplasticpolymers. In one or more embodiments, the thermoplastic polymer mayinclude a blend of olefinic polymers. Useful blends include thosedescribed in International Application No. PCT/US06/033522 which isincorporated herein by reference. For example, a particular blend mayinclude (i) a plastomer, (ii) a low density polyethylene, and (iii) apropylene-based polymer.

In one or more embodiments, propylene-based polymers may includepolypropylene homopolymer or copolymers of propylene and a comonomer,where the copolymer includes, on a mole basis, a majority of mer unitsderiving from propylene. In one or more embodiments, the propylene-basedcopolymers may include from about 2 to about 6 mole percent, and inother embodiments from about 3 to about 5 mole percent mer unitsderiving from the comonomer with the remainder including mer unitsderiving from propylene. In one or more embodiments, the comonomerincludes at least one of ethylene and an α-olefin. The α-olefins mayinclude butene-1, pentene-1, hexene-1, octene-1, or 4-methyl-pentene-1.In one or more embodiments, the copolymers of propylene and a comonomermay include random copolymers. Random copolymers may include thosepropylene-based copolymers where the comonomer is randomly distributedacross the polymer backbone.

The propylene-based polymers employed in one or more embodiments of thisinvention may be characterized by a melt flow rate of from about 0.5 toabout 15 dg/min, in other embodiments from about 0.7 to about 12 dg/min,in other embodiments from about 1 to about 10 dg/min, and in otherembodiments from about 1.5 to about 3 dg/min per ASTM D-1238 at 230° C.and 2.16 kg load. In these or other embodiments, the propylene-basedpolymers may have a weight average molecular weight (M_(w)) of fromabout 1×10⁵ to about 5×10⁵ g/mole, in other embodiments from about 2×10⁵to about 4×10⁵ g/mole, and in other embodiments from about 3×10⁵ toabout 4×10⁵ g/mole, as measured by GPC with polystyrene standards. Themolecular weight distribution of these propylene-based copolymer may befrom about 2.5 to about 4, in other embodiments from about 2.7 to about3.5, and in other embodiments from about 2.8 to about 3.2.

In one or more embodiments, propylene-based polymers may becharacterized by a melt temperature (T_(m)) that is from about 165° C.to about 130° C., in other embodiments from about 160 to about 140° C.,and in other embodiments from about 155° C. to about 140° C. In one ormore embodiments, particularly where the propylene-based polymer is acopolymer of propylene and a comonomer, the melt temperature may bebelow 160° C., in other embodiments below 155° C., in other embodimentsbelow 150° C., and in other embodiments below 145° C. In one or moreembodiments, they may have a crystallization temperature (T_(c)) ofabout at least 90° C., in other embodiments at least about 95° C., andin other embodiments at least 100° C., with one embodiment ranging from105° to 115° C.

Also, these propylene-based polymers may be characterized by having aheat of fusion of at least 25 J/g, in other embodiments in excess of 50J/g, in other embodiments in excess of 100 J/g, and in other embodimentsin excess of 140 J/g.

In one or more embodiments, the propylene-based polymers may becharacterized by a flexural modulus, which may also be referred to as a1% secant modulus, in excess of 120,000 psi, in other embodiments inexcess of 125,000, in other embodiments in excess of 130,000 psi, inother embodiments in excess of 133,000 psi, in other embodiments inexcess of 135,000 psi, and in other embodiments in excess of 137,000psi, as measured according to ASTM D-790.

Useful propylene-based polymers include those that are commerciallyavailable. For example, propylene-based polymers can be obtained underthe tradename PP7620Z™ (Fina), PP33BF01™ (Equistar), or under thetradename TR3020™ (Sunoco).

In one or more embodiments, plastomers include ethylene-α-olefincopolymers. The plastomer employed in one or more embodiments of thisinvention includes those described in U.S. Pat. Nos. 6,207,754,6,506,842, 5,226,392, and 5,747,592, which are incorporated herein byreference. This copolymer may include from about 1.0 to about 15 molepercent, in other embodiments from about 2 to about 12, in otherembodiments from about 3 to about 9 mole percent, and in otherembodiments from about 3.5 to about 8 mole percent mer units derivingfrom α-olefins, with the balance including mer units deriving fromethylene. The α-olefin employed in preparing the plastomer of one ormore embodiments of this invention may include butene-1, pentene-1,hexene-1, octene-1, or 4-methyl-pentene-1.

In one or more embodiments, plastomers may be characterized by a densityof from about 0.865 g/cc to about 0.900 g/cc, in other embodiments fromabout 0.870 to about 0.890 g/cc, and in other embodiments from about0.875 to about 0.880 g/cc per ASTM D-792. In these or other embodiments,the density of the plastomers may be less than 0.900 g/cc, in otherembodiments less than 0.890 g/cc, in other embodiments less than 0.880g/cc, and in other embodiments less than 0.875 g/cc.

In one or more embodiments, the plastomer may be characterized by aweight average molecular weight of from about 7×10⁴ to 13×10⁴ g/mole, inother embodiments from about 8×10⁴ to about 12×10⁴ g/mole, and in otherembodiments from about 9×10⁴ to about 11×10⁴ g/mole as measured by usingGPC with polystyrene standards. In these or other embodiments, theplastomer may be characterized by a weight average molecular weight inexcess of 5×10⁴ g/mole, in other embodiments in excess of 6×10⁴ g/mole,in other embodiments in excess of 7×10⁴ g/mole, and in other embodimentsin excess of 9×10⁴ g/mole. In these or other embodiments, the plastomermay be characterized by a molecular weight distribution (M_(w)/M_(n))that is from about 1.5 to 2.8, in other embodiments 1.7 to 2.4, and inother embodiments 2 to 2.3.

In these or other embodiments, the plastomer may be characterized by amelt index of from about 0.1 to about 8, in other embodiments from about0.3 to about 7, and in other embodiments from about 0.5 to about 5 perASTM D-1238 at 190° C. and 2.16 kg load.

The uniformity of the comonomer distribution of the plastomer of one ormore embodiments, when expressed as a comonomer distribution breadthindex value (CDBI), provides for a CDBI of greater than 60, in otherembodiments greater than 80, and in other embodiments greater than 90.

In one or more embodiments, the plastomer may be characterized by a DSCmelting point curve that exhibits the occurrence of a single meltingpoint break occurring in the region of 50 to 110° C.

The plastomer of one or more embodiments of this invention may beprepared by using a single-site coordination catalyst includingmetallocene catalyst, which are conventionally known in the art.

Useful plastomers include those that are commercially available. Forexample, plastomer can be obtained under the tradename EXXACT™ 8201(ExxonMobil); or under the tradename ENGAGE™ 8180 (Dow DuPont). In oneor more embodiments, the low density polyethylene includes anethylene-α-olefin copolymer. In one or more embodiments, the low densitypolyethylene includes linear low density polyethylene. The linear lowdensity polyethylene employed in one or more embodiments of thisinvention may be similar to that described in U.S. Pat. No. 5,266,392,which is incorporated herein by reference. This copolymer may includefrom about 2.5 to about 13 mole percent, and in other embodiments fromabout 3.5 to about 10 mole percent, mer units deriving from α-olefins,with the balance including mer units deriving from ethylene. Theα-olefin included in the linear low density polyethylene of one or moreembodiments of this invention may include butene-1, pentene-1, hexene-1,octene-1, or 4-methyl-pentene-1. In one or more embodiments, the linearlow density polyethylene is devoid or substantially devoid of propylenemer units (i.e., units deriving from propylene). Substantially devoidrefers to that amount or less of propylene mer units that wouldotherwise have an appreciable impact on the copolymer or thecompositions of this invention if present.

The linear low density polyethylene of one or more embodiments of thisinvention can be characterized by a density of from about 0.885 g/cc toabout 0.930 g/cc, in other embodiments from about 0.900 g/cc to about0.920 g/cc, and in other embodiments from about 0.900 g/cc to about0.910 g/cc per ASTM D-792.

In one or more embodiments, the linear low density polyethylene may becharacterized by a weight average molecular weight of from about 1×10⁵to about 5×10⁵ g/mole, in other embodiments 2×10⁵ to about 10×10⁵g/mole, in other embodiments from about 5×10⁵ to about 8×10⁵ g/mole, andin other embodiments from about 6×10⁵ to about 7×10⁵ g/mole as measuredby GPC with polystyrene standards. In these or other embodiments, thelinear low density polyethylene may be characterized by a molecularweight distribution (M_(w)/M_(n)) of from about 2.5 to about 25, inother embodiments from about 3 to about 20, and in other embodimentsfrom about 3.5 to about 10. In these or other embodiments, the linearlow density polyethylene may be characterized by a melt flow rate offrom about 0.2 to about 10 dg/min, in other embodiments from about 0.4to about 5 dg/min, and in other embodiments from about 0.6 to about 2dg/min per ASTM D-1238 at 230° C. and 2.16 kg load.

The linear low density polyethylene of one or more embodiments of thisinvention may be prepared by using a convention Ziegler Nattacoordination catalyst system.

Useful linear low density polyethylene includes those that arecommercially available. For example, linear low density polyethylene canbe obtained under the tradename Dowlex™ 2267G (Dow); or under thetradename DFDA-1010 NT7 (Dow); or under the tradename GA502023(Lyondell).

In one or more embodiments, useful thermoplastic vulcanizates includethose available under the tradename UniPrene (Teknor Apex)® andSantoprene (ExonMobil)®.

Useful ethylene alkyl-acrylates include those available under thetradename ELVALOY® (DuPont).

In one or more embodiments, block copolymers that may be used includestyrene-butadiene block copolymers such as, but not limited to,styrene-butadiene-styrene block copolymers. These block copolymers maybe blended with polyolefins such as polypropylene to form thermoplasticcompositions that are useful in the practice of this invention.

In one or more embodiments, still other useful thermoplastic materialsinclude propylene-based elastomers such as those available under thetradenames VISTAMAXX (Exxonmobil) and VERSIFY (Dow Chemical).

In one or more embodiments, the thermoplastic polymer or polymersforming the thermoplastic matrix in which the expandable graphite isdispersed has a melt temperature below 200° C., in other embodimentsbelow 180° C., in other embodiments below 160° C., and in otherembodiments below 150° C.

Other Ingredients

In addition to the expandable graphite and complementary flameretardants, the other additional ingredients may be dispersed in the oneor more layers of thermoplastic polyolefin. These additional ingredientsmay include processing aids, stabilizers, and/or other fillers.

In one or more embodiments, processing aides include those compoundsthat can be added to the thermoplastic polymer composition to assist inprocessing or to extend the polymeric materials. In one or moreembodiments, processing aids include those compounds that can reduce theviscosity and/or increase the flow of the thermoplastic polymer.Exemplary processing aids include metal salts of carboxylic acidsincluding metal salts of naturally occurring fats and oils. In one ormore embodiments, processing aids include calcium stearate and/or zincstearate. In other embodiments, processing aids include processing oilssuch as those that are conventional in plastics and/or rubberprocessing.

In one or more embodiments, the stabilizers may include one or more of aUV stabilizer, an antioxidant, and an antiozonant. UV stabilizersinclude Tinuvin™ 622. Antioxidants include Irganox™ 1010. In one or moreembodiments, carbon black is used as a stabilizer. Advantageously, thecarbon black may be used for this purpose at levels of less than 5 wt.%, in other embodiments less than 3 wt. %, and in other embodiments lessthan 2 wt. %, based on the entire weight of the composition.

Amounts

In one or more embodiments, the amount of expandable graphite includedwithin the thermoplastic polyolefin may be expressed with regard to thethermoplastic polyolefin. For example, in one or more embodiments, thecompositions (and/or layers) may include greater than 3 parts by weight,in other embodiments greater than 4 parts by weight, in otherembodiments greater than 5 parts by weight, in other embodiments greaterthan 10 parts by weight, and in other embodiments greater than 15 partsby weight expandable graphite per 100 parts by weight thermoplasticpolyolefin. In these or other embodiments, the compositions (and orlayers) may include less than 50 parts by weight, in other embodimentsless than 40 parts by weight, and in other embodiments less than 30parts by weight expandable graphite per 100 parts by weightthermoplastic polyolefin. In one or more embodiments, the compositions(and or layers) may include from about 3 to about 50 parts by weight, inother embodiments from about 4 to about 40 parts by weight, and in otherembodiments from about 5 to about 30 par parts by weight expandablegraphite per 100 parts by weight of the thermoplastic resin.

In one or more embodiments, the amount of expandable graphite includedwithin the thermoplastic polyolefin may be expressed with regard to thetotal weight of the composition or layer. For example, in one or moreembodiments, the compositions (and/or layers) may include greater than 3percent by weight, in other embodiments greater than 4 percent byweight, in other embodiments greater than 5 percent by weight, in otherembodiments greater than 10 percent by weight, and in other embodimentsgreater than 15 percent by weight expandable graphite based on theentire weight of the composition. In these or other embodiments, thecompositions (and or layers) may include less than 50 percent by weight,in other embodiments less than 40 percent by weight, and in otherembodiments less than 30 percent by weight expandable graphite based onthe entire weight of the composition. In one or more embodiments, thecompositions (and or layers) may include from about 3 to about 50percent by weight, in other embodiments from about 4 to about 40 percentby weight, and in other embodiments from about 5 to about 30 par percentby weight expandable graphite based on the entire weight of thecomposition.

Likewise, the amount of complementary flame retardant included withinthe thermoplastic polyolefin may be expressed with regard to thethermoplastic polyolefin. For example, in one or more embodiments, thecompositions (and or layers) may include greater than 3 parts by weight,in other embodiments greater than 5 parts by weight, and in otherembodiments greater than 10 parts by weight complementary flameretardant per 100 parts by weight thermoplastic polyolefin. In these orother embodiments, the compositions (and or layers) may include lessthan 50 parts by weight, in other embodiments less than 40 parts byweight, in other embodiments less than 30 parts by weight, and in otherembodiments less than 20 parts by weight complementary flame retardantper 100 parts by weight thermoplastic polyolefin.

Those skilled in the art will be able to readily select an appropriateamount of the other ingredients that may be used in the compositions ofthis invention. For example, the other ingredients such as theprocessing additives, UV stabilizers, and antioxidants may be used,although the amounts may vary, in amounts from about 0.1 to about 2percent, in other embodiments from about 0.5 to about 1.5 percent, andin other embodiments from about 0.7 to about 1.3 percent, based on thetotal weight of the composition. In particular embodiments, thecompositions including ground thermoset rubber include less than 10weight percent, in other embodiments less than 8 weight percent, inother embodiments less than 5 weight percent, and in other embodimentsless than 3 weight percent filler or flame retardant based on the entireweight of the thermoplastic polyolefin, ground rubber, andcompatibilizer.

Multi-Layered Membrane

In one or more embodiments, a multi-layered membrane is provided whereinone or more layers of the membrane include expandable graphite. Inparticular embodiments, the layers are laminated to one another andtherefore the membrane may be referred to as a laminate. In otherembodiments, the layers are co-extruded to one another, and thereforethe membranes may be referred to as co-extrudates. In yet otherembodiments, the membranes may include co-extruded layers and laminatedlayers. The term laminates may therefore be employed to refer to themembranes regardless of whether they are formed by lamination and/orco-extrusion.

In one or more embodiments, the expandable graphite is dispersedthroughout one or more layers of a multi-layered membrane wherein thelayers in which the expandable graphite is dispersed include low-meltthermoplastic polymers. In one or more embodiments, these low-meltthermoplastic polymers have a melt temperature below the one or morethermoplastic polymers contained in other layers. Stated another way,the thermoplastic matrix in which the expandable graphite is dispersedhas a melt temperature lower than the one or more layers that may bedevoid or substantially devoid of expandable graphite. In particularembodiments, the melt temperature of the thermoplastic matrix in whichthe expandable graphite is dispersed is at least 5° C., in otherembodiments at least 10° C., and in other embodiments at least 15° C.lower than one or more other layers of the multi-layered membrane.

In particular embodiments, the expandable graphite exists within theinner layer or layers of a multi-layered membrane. In other embodiments,the expandable graphite may exist in the lower layers of themulti-layered membrane, which include at least one of those layers thatare below the layer that is exposed to the environment when the membraneis installed. In other embodiments, the top layer, which is the layerexposed to the environment when the membrane is installed on a roof,includes the expandable graphite. In yet other embodiments, the toplayer is devoid of expandable graphite and is white or substantiallywhite in color, while one or more of the lower layers include expandablegraphite. This particular combination produces a membrane that is highlyadvantageous in several respects. First, the membrane exhibits improvedfire performance as a result of the expandable graphite being located inone or more of the layers. And, second, by having a white exteriorsurface, the membrane can reflect infrared radiation and thereby reduceenergy demands that may be required to cool the building that themembrane is covering. Moreover, the white exterior surface can reflectelectromagnetic radiation (e.g., ultraviolet radiation) that can have adeleterious impact on the inner layer or lower layers.

Embodiments of the present invention may be described with reference toFIG. 1. Multi-layered membrane 10 includes upper layer 12 and lowerlayer 14. An optional reinforcing scrim 16 may be positioned betweenupper layer 12 and lower layer 14. In one or more embodiments, upperlayer 12 and lower layer 14, together with optional scrim 16 sandwichedthere between, may be prepared by using lamination techniques. In one ormore embodiments, upper layer 12 may include expandable graphite. Inother embodiments, lower layer 14 may include expandable graphite. Inyet other embodiments, both upper layer 12 and lower layer 14 mayinclude expandable graphite.

In one or more embodiments, upper layer 12 may include two or moresub-layers. As the skilled person will recognize, this may beaccomplished by using co-extrusion techniques. For example, and as shownin FIG. 1, upper layer 12 includes top layer 22 and upper-middle layer24. Also, and as shown in FIG. 1, lower layer 14 may includelower-middle layer 26 and bottom layer 28. In one or more embodiments,at least one of top layer 22, upper-middle layer 24, lower-middle layer26, and bottom layer 28 includes expandable graphite in accordance withone or more embodiments of the present invention.

In particular embodiments, upper-middle layer 24 and optionallylower-middle layer 26 include expandable graphite. In these or otherembodiments, bottom layer 28 includes expandable graphite. In stillother embodiments, top layer 22 includes expandable graphite.

In yet other embodiments, as shown in FIG. 2, lower layer 14 is a singleextruded layer that is laminated to co-extruded layer 12, which includessub layers 22 and 24. In one or more embodiments, lower layer 14includes expandable graphite.

In particular embodiments, top layer 22, which may be the layer of thelaminate that is exposed to the environment when installed on a roof, iswhite or substantially white. In these or other embodiments, top layer22 is devoid or substantially devoid of expandable graphite, whileupper-middle layer 24 includes expandable graphite dispersed in athermoplastic polyolefin according to the present invention. Besides theabsence of the expandable graphite, top layer 22 may includethermoplastic polyolefin that is similar to or the same as thethermoplastic polyolefin in forming upper-middle layer 24. In otherembodiments, upper-middle layer 24 may include a thermoplasticpolyolefin that is distinct from top layer 22. Additionally, top layer22 may include other constituents that are conventionally employed inthermoplastic roofing membranes. As is known in the art, theseconstituents may include antioxidants, UV stabilizers, and the like.

As those skilled in the art appreciate, upper or top layer 22 can bewhite or substantially white through the inclusion of white fillers.These white fillers may include clay, talc, mica, and/or titaniumdioxide. For example, top layer 22 may include titanium dioxide in anamount of at least 3 percent by weight, in other embodiments at least 5percent by weight, or in other embodiments at least 7 percent by weight,based on the total weight of the top layer. In these or otherembodiments, top layer 20 may include less than 20 percent by weight, inother embodiments less than 15 percent by weight, and in otherembodiments less than 12 percent by weight titanium dioxide, based onthe total weight of the top layer.

In one or more embodiments, the white or substantially white layerexhibits a reflectivity of at least 65 percent, in other embodiments atleast 80 percent, and in other embodiments at least 85 percent, wherethe reflectivity is a measure of the reflectants of visible light. Inother embodiments, the reflectivity is a measure of visible and infraredelectromagnetic radiation. In other embodiments, the reflectivity is ameasure of the reflectants of visible light, infrared radiation, and UVradiation.

In one or more embodiments, the membranes of the present invention arecharacterized by a breaking strength, according to ASTM D751, of greaterthan 150 pounds force, in other embodiments greater than 220 poundsforce, and in other embodiments greater than 350 pounds force. In theseor other embodiments, the membranes of this invention are characterizedby a tearing strength, according to ASTM D751, of greater than 45 poundsforce, in other embodiments greater than 55 pounds force, in otherembodiments greater than 100 pounds force, and in other embodimentsgreater than 150 pounds force.

Method of Making

In one or more embodiments, the compositions and membranes of thepresent invention may be prepared by employing conventional techniques.For example, the various ingredients can be separately fed into areaction extruder and pelletized or directly extruded into membrane orlaminate sheet. In other embodiments, the various ingredients can becombined and mixed within a mixing apparatus such as an internal mixerand then subsequently fabricated into membrane sheets or laminates.

In one or more embodiments, the membranes of the present invention maybe prepared by extruding a polymeric composition into a sheet. Multiplesheets may be extruded and joined to form a laminate. A membraneincluding a reinforcing layer may be prepared by extruding at least onesheet on and/or below a reinforcement (e.g., a scrim). In otherembodiments, the polymeric layer may be prepared as separate sheets, andthe sheets may then be calandered or laminated with the scrim sandwichedtherebetween to form a laminate. In one or more embodiments, themembranes of the present invention are prepared by employingco-extrusion technology. Useful techniques include those described inco-pending U.S. Ser. Nos. 11/708,898 and 11/708,903, which areincorporated herein by reference.

Following extrusion, and after optionally joining one or more polymericlayers, or optionally joining one or more polymeric layer together witha reinforcement, the membrane may be fabricated to a desired thickness.This may be accomplished by passing the membrane through a set ofsqueeze rolls positioned at a desired thickness. The membrane may thenbe allowed to cool and/or rolled for shipment and/or storage.

The polymeric composition that may be extruded to form the polymericsheet may include the ingredients or constituents described herein. Forexample, the polymeric composition may include thermoplastic polyolefinand the expandable graphite. The ingredients may be mixed together byemploying conventional polymer mixing equipment and techniques. In oneor more embodiments, an extruder may be employed to mix the ingredients.For example, single-screw or twin-screw extruders may be employed.

In one embodiment, each of the polymeric ingredients (e.g.,thermoplastic polyolefin) may be added to the extruder at the feedthroat of the extruder. The filler and other ingredients (e.g.,expandable graphite) that may be desirable may be added at the feedthroat or within a subsequent stage or barrel of the extruder (e.g.,downstream of the feed throat). This can be accomplished, for example,by using a side feeder. One or more of the polymeric ingredients mayalso be added downstream of the feed throat. This may include partialaddition at the feed throat and partial addition downstream, or completedownstream addition of one or more polymeric ingredients.

In one or more embodiments, the thermoplastic polyolefin including theexpandable graphite is processed at temperatures above the meltingpoint, or in other embodiments above the processing temperature of thepolyolefin or thermoplastic material used to form the sheet. In one ormore embodiments, the thermoplastic is processes at temperatures inexcess of 150° C., in other embodiments in excess of 160° C., and inother embodiments in excess of 170° C., in other embodiments in excessof 220° C., and in other embodiments in excess of 230° C. to obtain afree-flowing melted composition, but below the expansion temperature ofthe expandable graphite (e.g. temperatures below 250° C., in otherembodiments below of 220° C., in other embodiments below 180° C., and inother embodiments below 180° C.). Once this is achieved, the compositioncan be conveyed downstream within the extruder under low shear such asmay be achieved by using conveying elements in the absence orsubstantial absence of kneading elements. In one or more embodiments,the thermoplastic polyolefin, together with other optional ingredientsbesides the expandable graphite, are processed at higher temperaturesand mixing energies, and then the expandable graphite is subsequentlyintroduced to the composition, such as may occur by the addition of theexpandable graphite at a downstream barrel. This also can occur underlow shear conditions such as may be achieved by the use of conveyingelements in the absence or substantial absence of kneading elements. Inaddition to the expandable graphite, oil can be added together with theexpandable graphite. For example, a pre-blend of expandable graphite andoil can be injected into the extruder at a desirable downstreamlocation.

INDUSTRIAL APPLICABILITY

The membranes of one or more embodiments of the present invention areuseful in a number of applications. In one embodiment, the membranes maybe useful for roofing membranes that are useful for covering flat orlow-sloped roofs. In other embodiments, the membranes may be useful asgeomembranes. Geomembranes include those membranes employed as pondliners, water dams, animal waste treatment liners, and pond covers.

As described above, the membranes of one or more embodiments of thepresent invention may be employed as roofing membranes. In one or moreembodiments, these membranes include thermoplastic roofing membranesincluding those that may meet the specifications of ASTM D-6878-03.These membranes maybe employed to cover flat or low/sloped roofs. Theseroofs are generally known in the art as disclosed in U.S. Ser. Nos.60/586,424 and 11/343,466, and International Application No.PCT/US2005/024232, which are incorporated herein by reference. As shownin FIG. 4, a flat or low-sloped roof assembly 80 may include a roof deck32, and optional insulation layer 34, and membrane 10 according to thepresent invention.

Practice of this invention is not limited by the selection of anyparticular roof deck. Accordingly, the roofing systems herein caninclude a variety of roof decks. Exemplary roof decks include concretepads, steel decks, wood beams, and foamed concrete decks.

Practice of this invention is likewise not limited by the selection ofany particular insulation board. Moreover, the insulation boards areoptional. Several insulation materials can be employed includingpolyurethane or polyisocyanurate cellular materials. These boards areknown as described in U.S. Pat. Nos. 6,117,375, 6,044,604, 5,891,563,5,573,092, U.S. Publication Nos. 2004/0109983 2003/0082365,2003/0153656, 2003/0032351, and 2002/0013379, as well as U.S. Ser. Nos.10/640,895, 10/925,654, and 10/632,343, which is incorporated herein byreference.

In other embodiments, these membranes may be employed to cover flat orlow-slope roofs following a re-roofing event. In one or moreembodiments, the membranes may be employed for re-roofing as describedin U.S. Publication No. 2006/0179749, which are incorporated herein byreference.

What is claimed is:
 1. A multi-layered membrane comprising: i. a firstthermoplastic first layer; and ii. a second thermoplastic layer, wherethe second layer includes expandable graphite.
 2. The membrane of claim1, where the membrane further includes a reinforcing scrim.
 3. Themembrane of claim 1, where the first and second layers are laminated toone another.
 4. The membrane of claim 1, where the first layer includesat least two sub-layers that are formed by co-extrusion.
 5. The membraneof claim 4, where at least one of the layers formed by co-extrusionincludes the expandable graphite.
 6. The membrane of claim 1, where thesecond layer includes at least two sub-layers that are formed byco-extrusion.
 7. The membrane of claim 6, where at least one of thelayers formed by co-extrusion includes the expandable graphite.
 8. Themembrane of claim 1, where the second thermoplastic layer includes athermoplastic polymer, and where the second layer includes at least 5parts by weight expandable graphite per 100 parts by weight of thethermoplastic polymer.
 9. A multi-layered thermoplastic membranecomprising: at least one thermoplastic layer having dispersed thereinexpandable graphite.
 10. The membrane of claim 9, where the at least onelayer includes at least 3 percent by weight expandable graphite based onthe entire weight of the layer.